737 Flight Crew Operations Manual
Flight Management, Navigation -
Flight Management Computer
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
D6-27370-866-EGP 11.32.3
With derated takeoff selected, the thrust setting parameter is considered a
limitation for takeoff; therefore, thrust levers should not be advanced further
except in an emergency. A further thrust increase following an engine failure
could result in a loss of directional control while on the ground. Use the takeoff
speeds supplied by the FMC or specified in Chapter PI, Performance-Inflight, for
the selected derate condition.
Derated takeoff rating can be further reduced by assumed temperature.
Use the takeoff speeds provided by the FMC or specified in Chapter PI,
Performance–Inflight, for the selected derate or variable takeoff rating condition.
Assumed Temperature Thrust Reduction Takeoff
A takeoff thrust less than the full rated thrust may be achieved by using an
assumed temperature that is higher than the actual temperature. The desired thrust
level is obtained through entry of a SEL TEMP value on the N1 LIMIT page or
TAKEOFF REF page 2. Use approved sources for selecting the assumed
temperature.
The maximum thrust reduction authorized is 25 percent below any certified rating.
Do not use assumed temperature reduced thrust if conditions exist that affect
braking, such as slush, snow, or ice on the runway, or if potential windshear
conditions exist.
If the assumed temperature method is applied to a fixed derate, application of
additional power should not exceed the fixed derate N1 limit as loss of directional
control could occur while on the ground.
When the assumed temperature method is used with full rate, the reduced thrust
setting is not considered a limitation. If conditions are encountered where
additional thrust is desired, the crew can manually apply full thrust.
Derated Thrust Climb
Two fixed climb thrust derates can be selected on the N1 LIMIT page. CLB–1
provides a climb limit reduced by 3% N1 (approximately 10% thrust). CLB–2
provides a climb limit reduced by 6% N1 (approximately 20% thrust). The
reduced climb setting gradually increases to full rated climb thrust by 15,000 feet.
In cruise, the thrust reference automatically changes to CRZ. The reference can be
manually selected on the N1 LIMIT page.
Use of an assumed temperature reduced thrust takeoff or takeoff derate affects the
FMCs climb derate computation. If a reduced thrust takeoff has been specified on
the TAKEOFF REF page, the FMC will re-compute CLB-1 and CLB-2 values as
required to avoid a climb N1 value greater than the reduced thrust takeoff N1
value.
September 26, 2013
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